1. Field of the Invention
The present invention relates to ceramic sintered bodies of which main component is a sialon with high fracture toughness value and relates to the method of producing the same.
2. Description of the Related Art
Sialon type sintered bodies of which main component is Si-Al-O-N have excellent characteristics of such as small coefficient of thermal expansion, high heat resistance, high acid resistance, and high erosion resistance. The sialon type sintered bodies have been used as structural materials like Si.sub.3 N.sub.4 group sintered bodies, SiC group sintered bodies, and so forth.
The sialon type sintered bodies have excellent characteristics of such as small degradation of strength in high temperature range and high acid resistance in comparison with the Si.sub.3 N.sub.4 group sintered bodies. On the other hand, the sialon type sintered bodies have a disadvantage of lower reliability as a structural material than the Si.sub.3 N.sub.4 group sintered bodies. To improve the reliability of the sialon type sintered bodies, particles which are not solid solved in a sialon type sintered body, for example, particles of SiC, have been dispersed therein. An object of this attempt was to improve the fracture toughness value by a complex effect along with dispersed particles.
The sialon type sintered bodies in which different particles of such as SiC are dispersed and contained can be produced by adding different particles of such as SiC to powder satisfying a sialon composition (hereinafter named sialon powder). However, when the different particles of such as SiC are added to sialon powder, the sintering characteristic of the sialon powder is remarkably degraded. Thus, so far, when a pressure-free sintering method such as normal pressure sintering method was used, at most around 5 parts by weight of SiC or the like as dispersed particles could be added to 100 parts by weight of sialon powder. If more parts of SiC or the like were added, sintered bodies could not be constructed with high density by the pressure-free sintering method. Thus, so far, the effect of improving the fracture toughness value due to dispersed particles could not be satisfactorily accomplished by the conventional method.
On the other hand, by using a hot press method, it is possible to add around 50 parts by weight of SiC particles or the like to 100 parts by weight of sialon powder. However, the hot press method has the following disadvantages. In other words, when the hot press method is used, the shapes of products are limited to simple ones. In addition, the hot press method is not suitable for mass production due to a high production cost. Moreover, even if the hot press method is used, the fracture toughness value which can be obtained is not satisfactory. Furthermore, even if HIP method or the like is used, a remarkable effect cannot be achieved.
In comparison with the hot press method, the pressure-free sintering method has advantages of high degree of freedom with respect to shapes of sintered bodies, a low production cost, and suitability of mass production. Thus, it was strongly desired to provide sialon type sintered bodies with high fracture toughness value by using the pressure-free sintering method.